1. Field of the Invention
The present invention relates to a honeycomb structure, in which plugging portions are formed in the ends of cells, and a manufacturing method of the honeycomb structure.
2. Description of the Related Art
In consideration of influences on environments, there has been an increasing need to remove, from an exhaust gas, a particulate matter contained in the exhaust gas discharged from an internal combustion engine such as an engine for a car, an engine for a construction machine or a stationary engine for an industrial machine, other combustion devices or the like. In particular, regulations on the removal of the particulate matter (PM) discharged from a diesel engine tend to be strengthened worldwide. Because of such a situation, a diesel particulate filter (DPF) for collecting and removing the particulate matter attracts attention.
Examples of the DPF include a honeycomb filter having porous partition walls for partitioning a plurality of cells constituting fluid channels from one another. In the honeycomb filter, predetermined cells each having one open end and the plugged other end and remaining cells each having one plugged end and the other open end are alternately arranged, and a catalyst is carried by the inner surfaces of pores in the partition walls. When such a honeycomb filter is applied as the DPF, a fluid (the exhaust gas) which has flowed into the predetermined cell from the one open end thereof passes through the partition walls, and flows out as the passed fluid toward the remaining cells. Furthermore, the gas is discharged from the other open end of the remaining cell, whereby the particulate matter in the exhaust gas is oxidized and decomposed by the catalyst, and collected and removed by the pores.
On the other hand, a thermal shock stress is easily concentrated on a boundary between the partition wall and each plugging portion, and a crack is easily generated in the boundary. To solve the problem, a filter having a constitution in which the plugging portions substantially have non-uniform plugging thicknesses has been known (see JP-A-8-281034).
Furthermore, there has been known a honeycomb structure in which the sectional open ratio of a plugging portion in the vicinity of the partition wall is set to a ratio smaller than that of another plugging portion in the vicinity of a central axis, so that the breakdown of the plugging portion or the vicinity of the plugging portion due to the thermal shock is not easily caused (see JP-A-2006-116483).
However, in JP-A-8-281034, a large number of steps are required for the preparation of the filter. Moreover, in JP-A-2006-116483, any problem does not occur in a bonding strength between the plugging portion and the partition wall. However, in respect of a collection efficiency, according to comparison between a case where there is not any gap between the plugging portion and the partition wall and a case where the gap is present over the whole length of the plugging portion as especially shown in FIG. 3, a difference in a collection mass is hardly made, but a large difference in the number of the collected PMs is made.